Appliance with an ic card reader and overload protection

ABSTRACT

The appliance comprises an IC card reader for an operation with an IC card and a power supply for providing a supply voltage, in particular for the IC card. The appliance comprises further an overload protection circuit, which simulates an IC card extraction in case of an overload of the supply voltage. The power supply is then immediately switched off to avoid any damage for the power supply. In a preferred embodiment, the IC card reader is equipped with a card presence switch for indicating to a micro-controller of the appliance, that an IC card has been inserted into the card reader. The micro-controller provides then a control signal for switching on the power supply for the operation with the IC card. The protection circuit is coupled between the supply voltage for the IC card and the signal line of the card presence switch and provides a detection of a short circuit. The protection circuit may comprise a diode, a comparator or a transistor, which switches off the power supply via a logic circuit.

The present invention relates to an appliance having an IC card readerfor operation with an IC card. Appliances of this kind are known forexample from pay television broadcast (pay TV), electronic payment, orbanking services.

IC cards, also known as smart cards, are portable information media,having the size of about a credit card. They comprise an integrated cardcontroller, or at least an integrated memory, for a data exchange with arespective appliance. A portable device of this kind is known forexample from EP-A-0 633 544. As a general term for this data media theexpression “IC card” will be used throughout in this description. ICcards are usually provided with contacts being mechanically contacted byan IC card reader for an electrical connection for the data exchangewith the respective appliance.

The communication between IC cards and respective appliances with ICcard readers is described for example in WO 97/25685 and EP-A-0 814 427.An international standard, which describes and defines IC cards havingcontacts and the operation procedures of IC cards, is ISO/IEC7816-3:1997(E). This standard is used particularly for pay televisionsystems, which use a set-top box or a digital satellite receiver with anIC card reader and respective IC cards for authorizing the reception ofpay television broadcasts. The respective IC cards comprise data, whichenable the set-top box to unscramble received coded video signals.

In appliances using an IC card reader, there is a possibility that ashort circuit occurs, when inserting the IC card into the card reader,for example when the IC card is damaged, or when there is moisture onthe IC card. Standards like ISO/IEC 7816 or EMV2000 require therefore aprotection of the supply voltage against short circuits. A widely usedinterface IC TDA8004, made for example by Philips Semiconductors, hastherefore a short circuit protection already included. This integratedcircuit provides many functions and is therefore comparativelyexpensive.

An overcurrent protection circuit for a power supply providing an ICcard with power is disclosed in U.S. Pat. No. 5,977,758. This circuitcomprises a current detection circuit, which switches in case of amalfunction the power to the IC card off independently of amicro-controller.

It is an object of the invention to provide an appliance having an ICcard reader and an overload protection, which provides a highreliability.

This object is achieved by an appliance as specified in claim 1.Advantageous developments of the invention are specified in thesubclaims.

According to the invention, the appliance comprises an IC card readerfor an operation with an IC card and a power supply for providing asupply voltage, in particular for the IC card reader. The appliancecomprises further an overload protection circuit, which simulates an ICcard extraction in case of an overload of the supply voltage. The powersupply is then immediately switched off to avoid any damage for thepower supply.

In a preferred embodiment, the IC card reader is equipped with a cardpresence switch for indicating to a micro-controller of the appliance,that an IC card has been inserted into the card reader. Themicro-controller provides then a control signal for switching on thepower supply for the operation with the IC card. Power to the IC card istherefore only provided, when a signal of the card presence switchindicates that an IC card has been inserted. In case of an overload ofthe supply voltage, the overload protection circuit changes the positivesignal of the card presence switch to a value, which states that no ICcard is present. Therefore, an extraction of the IC card is simulated.

In a further preferred embodiment, the overload protection circuit iscoupled between the supply voltage for the IC card and the signal lineof the card presence switch and provides a detection of a short circuit.The protection circuit may comprise a diode, a comparator or atransistor, which resets the value of the card presence switch to avalue, which simulates that no IC card is present.

Advantageously, a logic circuit is used, to control the switching on andoff of the power supply for the IC card. To this circuit the cardpresence signal and the power on/off signal from the micro-controllerare coupled and the operation of the logic circuit is such, that thepower supply is only switched on, when an IC card is inserted applying apositive signal from the card presence switch to the logic circuit, andwhen the micro-controller provides the command signal for switching onthe supply voltage. Then the logic circuit switches through for turningthe power to the IC card on. The logic circuit is for example an ANDcircuit or a NAND circuit. When a short circuit occurs, the power to theIC card is immediately switched off via the logic circuit, independentlyfrom the micro-controller. The power is therefore switched off muchfaster, as could be performed by the micro-controller, which reduces thedanger of damaging the power supply.

Preferred embodiments of the invention are now explained in more detailwith reference to schematic drawings, which show:

FIG. 1 An appliance with an IC card reader and an overload protectioncircuit, and

FIG. 2 an appliance with an IC card reader comprising a protectioncircuit against a short circuit.

The appliance shown in FIG. 1 comprises an IC card reader 3, which ispowered by a power supply 4 via line 8. The IC card reader 3 comprisesin particular a housing, in which a respective IC card can be inserted,and contact terminals for applying a supply voltage VCC to the IC cardand for providing an exchange of digital data between the IC card and amicro-controller 5 of the appliance. The card reader 3 comprises furthera card presence switch 2, which provides a signal “CARD-DET” via asignal line 7 to the micro-controller 5, when an IC card is inserted.The card presence switch 2 is a mechanical switch, which is operated,when an IC card is inserted. If an IC card is inserted, the switch 2 isopened. Via a respective circuitry, as explained with regard to FIG. 2,a logical “HIGH” signal, “CARD-DET”, is provided then to themicro-controller 5.

According to the invention, an overload protection circuit 6 is coupledbetween the line 8 of the supply voltage VCC and the line 7 of the carddetect signal, which converts in case of an overload of the supplyvoltage VCC the signal indicating the presence of an inserted IC card toa value, which states that no IC card is present. The overload of thesupply voltage VCC simulates therefore via the protection circuit 6 anIC card extraction for switching off the power supply 4.

The power supply 4 in this embodiment is switched on and off by a logiccircuit IC3, to which inputs the signal from the card presence switch 2“CARD-DET” is applied and the power on/off signal “CMD-VCC” from themicro-controller 5. The power supply 4 is then switched on only, when apositive signal from the card presence switch 2 is provided and a poweron command from the micro-controller 5. In case of an overloadcondition, the protection circuit 6 converts the signal from the cardpresence switch 2 from “CARD DETECTED” to “NO CARD PRESENT”, andtherefore switches off the power supply 4 immediately via the logiccircuit IC3. The logic circuit IC3 is for example a NAND or an ANDcircuit.

The protection circuit 6 may comprise an over-current protectioncircuit, which measures the current of line 8 for example via ameasuring resistor, and which provides a respective signal for anoverload, when the current provided by the power supply 4 is too high.In another embodiment, the protection circuit 6 comprises a voltagedetector for the supply voltage VCC, which uses a voltage threshold fordetermining a breakdown of the supply voltage VCC. This can be performedfor example by a protection circuit comprising a comparator, atransistor or a diode, or by any other switching element. A supplyvoltage breakdown occurs for example in case of a short circuit.

In FIG. 2 a detail of a digital set-top box is shown comprising an ICcard reader 3 and relevant parts for the operation of the set-top boxwith an IC card. The IC card reader 3 comprises an IC card connector 1with contacts C1-C8, for operation with an IC card according to the IEC7816-3:1997(E) standard. The contacts C1-C8 provide the followingconnections to an IC card: C1 for supply voltage VCC, C2 for a reset ofthe IC card, C3 for providing a clock signal CLK to the IC card, C4, C5and C8 for providing ground terminal connections to the IC card, C6(reserved for a programming voltage VPP) and C7 for providing a datainput/output connection for a data exchange between the IC card and theset-top box.

The set-top box comprises further an integrated circuit IC1, a bufferand line driver for the digital signals used for operation with the ICcard. The respective signals, which are coupled to the integratedcircuit 1, are the reset signal “RESET-CARD” for contact C2, the clocksignal “CLK-CARD” for contact C3, and data input and output signals“DOUT” and “DIN” for contact C7. The integrated circuit IC1 is forexample an integrated circuit 74HCT244 from Texas Instruments. For theIC1, also for the IC card and the electronics of the IC card reader 4, asupply voltage of 5 Volts is used.

The IC card reader 3 comprises a card presence switch 2 with switchcontacts SW for a detection of an IC card, when an IC card is insertedinto the IC card connector 1. To one of the switch contacts, PRES, asupply voltage of 5 V is coupled via a resistor R1. When an IC card isinserted into the IC card connector 1, the switch contacts SW are open.Also a transistor T1 is coupled via its base terminal to the switchcontact PRES. The transistor T1 provides therefore a “LOW” outputsignal, when the switch 2 is open, (IC card inserted) and a “HIGH”output signal, when the switch 2 is closed.

To the transistor T1 a NAND circuit IC2 is coupled, which is arranged asan inverter, for providing a signal “CARD-DET” for a micro-controller,not shown in FIG. 2, of the set-top box. The micro-controller is forexample a “system-on-chip” controller STI5516 from ST Microelectronics.The output signal of the NAND circuit IC2 is therefore “HIGH”, when anIC card is inserted. The output of IC2 is also coupled to an input of aNAND circuit IC3, for providing a supply voltage VCC to the IC card,terminal C1. To the other input of the NAND circuit IC3 a control signal“CMD-VCC” from the micro-controller is coupled. Therefore, when an ICcard has been inserted and then the control signal “CARD-DET” isprovided, the micro-controller provides the signal “CMD-VCC” forswitching on the supply voltage VCC for the IC card. The supply voltageVCC is provided by a transistor T2, to which base terminal the output ofIC3 is coupled. When the output of the NAND gate IC3 switches to “LOW”,transistor T2 switches through for supplying a 5 V supply voltage VCC tothe contact C1 of the IC card connector 1.

Between the line providing the supply voltage VCC to the contact C1 andthe line coming from the switch contact PRES of card presence switch 2 adiode D1 is coupled, which is arranged such, that the diode D1 conducts,when the signal from the switch contact is “HIGH”, but the supplyvoltage VCC is low. Therefore, when the supply voltage VCC breaks downwhen an IC card is inserted, for example when the IC card has a shortcircuit between respective IC card contacts, the diode D1 switchesthrough and therefore switches off transistor T1. Then the output ofNAND circuit IC2 switches to “LOW”, which switches off immediately thetransistor T2 via NAND circuit IC3. The transistor T2, the power supplyfor the IC card, is switched off therefore immediately by transistor T1and NAND circuits IC2 and IC3, and will not be damaged by a shortcircuit. There is a much smaller delay, as would be the case when thetransistor T2 would be switched off via the micro-controller. The diodeD1 provides therefore a very effective short circuit protection.

Instead of NAND circuits IC2 and IC3, also buffer/line driver circuitswith a controllable output can be used, for example integrated circuitsQuad buffer/line driver 74HC125 or 74HC126, manufactured for examplefrom Philips Semiconductors. These circuits comprise four non-invertingbuffers, which outputs are controllable via a respective output enableinput, the 74HC125 having active LOW enable inputs and the 74HC126active HIGH enable inputs.

The overload protection circuit 6, FIG. 1, may be arranged also within apower supply circuit, which provides then an error signal in case of anoverload. For example, an adjustable power voltage regulator LP2951 fromFairchild Semiconductor Corporation can be used, which provides an errorsignal in case of a low output voltage, which may occur for example incase of a short. The IC LP2951 is switched on and off via the signalCMD-VCC from micro-controller 5, see FIG. 1.

The error signal from IC LP2951 can be applied for example to the outputenable input of a buffer/line driver circuit, IC 74HC125, to which inputthe card detected signal CARD-DET, FIG. 1, is coupled, and which outputis coupled to IC3 and to the micro-controller 5. In case of an overloadof the supply voltage VCC, the error signal from IC LP2951 then changesthe output from the buffer/line driver circuit from positive tonegative, simulating therefore an IC card extraction, which switches offthe power supply 4 via IC3.

The overload protection as described is especially suited for a digitalset-top box or a satellite receiver operating with an IC card, butapplications for other appliances having an IC card reader for operationwith an IC card are also possible. The appliance may have also furtherIC card readers, which are protected in the same way.

1. Appliance comprising an IC card reader and a power supply forproviding a supply voltage, wherein the appliance comprises an overloadprotection circuit, which simulates an IC card extraction in case of anoverload of the supply voltage.
 2. Appliance according to claim 1,wherein the IC card reader comprises a card presence switch, and that incase of an overload of a the supply voltage, the overload protectioncircuit changes a card detected signal from positive to negative forsimulating an IC card extraction.
 3. Appliance according to claim 2,wherein the overload protection circuit is coupled to the card presenceswitch and to the supply voltage for a detection of an overload of thesupply voltage.
 4. Appliance according to claim 3, wherein the overloadprotection circuit comprises a diode, a comparator or a switch, beingarranged for detecting a voltage breakdown of the supply voltage. 5.Appliance according to claim 1, wherein to inputs of a switching means acard detected signal and a supply voltage “ON/OFF” command provided by amicro-controller is coupled, for switching on the power supply only,when the card detected signal is positive.
 6. Appliance according toclaim 5, wherein the switching means is a logic circuit gate, forexample a NAND or an AND circuit, or a buffer/line driver circuit withan output enable input.
 7. Appliance according to claim 1 wherein thatthe overload protection circuit is arranged within the power supplycircuit, which provides an error signal in case of an overload, and thatin case of an overload of the respective supply voltage, the errorsignal changes via a logic circuit a card detected signal from positiveto negative for simulating an IC card extraction.
 8. Appliance accordingto claim 1, wherein the supply voltage is a supply voltage for the ICcard reader, in particular for an IC card contact.
 9. Applianceaccording to claim 1, wherein the appliance is a digital set-top box ora digital satellite receiver with a respective IC card reader.